Zinc-bromine battery with circulating electrolytes

ABSTRACT

Zinc-bromine battery with circulating electrolytes, motor-driven pumps with pump chambers, containers for the electrolytes, dipolar electrodes and separators of synthetic material fitted between them, in which the edges of the separators and the electrodes are welded together, and electrolyte inlet and outlet lines allocated to the electrode chambers thus formed, and possibly heat exchangers for the electrolytes. One gas and liquid-proof chamber unit with at least one container, catholyte inlet and outlet lines, a pump chamber and cathode chambers is formed which is connected to another gas and liquid-proof chamber unit consisting of another container, anolyte inlet and outlet lines, another pump chamber and anode chambers, especially solely via separators.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a zinc-bromine battery with circulatingelectrolytes, motor-driven pumps with pump chambers, containers with apressure equalization for the electrolytes, bipolar electrodes andseparators disposed between them, which are constructed of plastic,wherein the frames of the separators and the frames of the electrodeshaving a greater thickness than the center part of the electrodes arewelded together and electrolyte supply and return lines associated withthe electrode chambers formed in this way and, if required, heatexchangers for the electrolytes.

2. Description of Background and Relevant Invention

The electro-chemical pairing of zinc and bromine is of increasingimportance for the accumulation of current. These systems are usedstationary for the accumulation of current in place of emergencypower-generating units, such as Diesel engines and generators, forexample, but also as an energy source for traction. In both cases weightis not of preponderant importance, but additional units can be employedas with the zinc-bromine battery.

However, zinc-bromine batteries are also known wherein not only the zincis stored at the electrode, but in this case the precipitated bromine ispresent in a porous mass of activated charcoal. The storage capacity ofsuch batteries is extraordinarily small and dentrites in the course ofthe precipitation of zinc are particularly disturbing, so that only lowcurrent densities can be employed.

Zinc-bromine batteries with two circulating electrolyte fluids have twoparticular advantages. On the one hand, interference because of thegrowth of dentrites is kept low and on the other hand it is possible toparticipate in the determination of the capacity of the battery by meansof the amounts of circulating electrolytes.

The material for producing a zinc-bromine battery was changed more andmore to the use of plastics, in particular polyolefins and in this casepolypropylene. These plastics have excellent chemical resistance but, onthe other hand, have various disadvantages. It is necessary to designthe electrodes as well as the separators as particularly thin-walledelements, on the one hand for reasons of electrical resistance, on theother hand to minimize the use of material. However, with suchthin-walled elements there is the disadvantage that the desiredgeometrical shape, a plane as a rule, leads to undesirable preferredflow forms even from small causes, for example different temperatures inthe electrolyte or pressure differences between the anolyte and thecatholyte. In this case it is necessary to take into consideration thatthe electrolytes flow through chambers having, for example, an area of30 cm ×30 cm, and the layer thickness of the flow can be from 1 mm to 2mm. If deformations in the plastic occur, the mentioned irregularitiesin the flow appear, because of which different precipitations anddissolution of the zinc film occur, wherein it is possible for localheating to appear which, in turn, can result in the prematuredestruction of the battery.

In connection with zinc-bromine batteries made from plastics it isfurthermore known that leaky spots occur again and again, for example atthe edges of the electrodes and separators, even under strong mechanicalpressure at the places to be sealed, so that such batteries cannotalways be used.

A galvanic element, in particular a rechargeable zinc-bromine battery,is known from EP 438 044, wherein the connecting line for pressureequalization terminates in the area of the highest point of thecollecting line when the element is in the normal position. It isdisadvantageous in this case that the electrolyte can run out if theelement is tilted, for example by 90°. Possible contamination of theenvironment by the electrolyte would have incalculable consequences.

SUMMARY OF THE INVENTION

It is the object of the instant invention to create a zinc-brominebattery which is suitable for the most diverse employment. It isintended in particular to create a small unit which can supply, forexample, 150 to 500 watt/hours, and thus allows the long operation ofvarious electrical consumers, for example drills, lawnmowers, but alsoradios, transmitters, television sets and the like.

The zinc-bromine battery in accordance with the invention is based on astate of the art as represented by EP-B1 0 167 517.

The zinc-bromine battery in accordance with the invention isdistinguished in that by means of respectively one container, catholytesupply and return lines, pump with a further container, anolyte supplyand return lines, a further pump chamber and anode chambers, isexclusively connected via separators, and that two chambers are providedbetween the two electrolyte containers for pressure equalization, whichare separated from each other by a rubber-elastic diaphragm.

By employing electrodes and separators made of plastic, materials whichhave been proven in connection with zinc-bromine batteries could beused, wherein the connection of the edges, be it by means of weldingwith or without additional welding materials, i.e. that for example anadditional film made from the material of the separators is appliednormally in connection with the extent of the separators and electrodes,wherein simultaneously the edges are also brought to melting and areconnected. As it is known, the employment of bipolar electrodes makes,on the one hand, higher voltages possible, and on the other hand theneed for space is minimized by this. For extreme conditions it may beadvantageous to take into account the temperature control, in particularcooling, of the electrolyte fluids via heat exchangers.

Due to the fact that respective gas- and fluid-proof spatial units areformed which, in particular exclusively, are connected via theseparators, a battery is created which assures operation even underunfavorable conditions, wherein at the same time no leakages of theelectrolyte fluid can occur, so that a battery with particularly lowmaintenance requirements is provided. In this connection it is ofparticular advantage that with such a battery, even if it is notmaintained, for example charged, during storage as required with otherbatteries, no destruction of the system occurs, instead it is onlynecessary for storing the battery to connect it again to a chargingdevice, so that the original capacity is again achieved.

If pressure equalization is provided between both electrolytecontainers, a deformation of the electrodes and separators as a resultof pressure differences can be particularly easily prevented, even withdifferent pressure generation in the electrolytes such as can occur, forexample, because of irregular pump operation, clogs in the lines, or thelike.

If both pumps are driven by one motor, this provides on the one hand aweight savings in a particularly simple manner wherein, on the otherhand, even flow speeds of the anolyte as well as for the catholyte areprovided.

If the fluid take-up capability of the containers at least correspondsto the respective amounts of anolyte and catholyte, discharge of thebattery during prolonged periods of idleness can be prevented byremoving the electrolyte from the electrode chambers.

If the containers are arranged next to each other in relation to theelectrodes, it is possible to provide a particularly simple structuralembodiment in respect to the flow since, for example, the pumps can bedisposed in an advantageous fluidic manner. A further advantage consistsin that a simple draining of the electrolyte from the electrolytechambers can be performed by a simple tilting of the battery, i.e. anarrangement of the battery in the form where the containers are at thebottom and the electrodes on the top, provided that essentially theentire amount of electrolyte can be received in the containers.

A particularly advantageous embodiment of the battery in accordance withthe invention is provided if in the operational state of the battery thecontainers for the electrolyte fluid are disposed above the electrodes,because in that case a particularly good flow through the electrodechambers can be performed, while taking the possibly occurring gasbubbles into consideration.

If the container has a closeable opening for removing and replenishingthe electrolyte fluid, it is possible, for example, to store thezinc-bromine battery, i.e. purely the plastic parts with the pump andthe like, dry for sales purposes, and only filling with electrolyteneeds to be performed at the place of use.

A particularly simple and compact embodiment of the battery results ifthe separators and/or the electrodes have continuous openings at theiredges, for example the welded frames, which are matched to each otherand form the electrolyte supply or return lines, each of which hasbranch lines into the electrode chambers. By means of such an embodimentit is possible to achieve a particularly compact battery, wherein at thesame time additional lines which are present outside the package caneither be completely avoided or reduced to a minimum.

If an electric fuse is disposed between the end contact of an electrodeand the drain of an electrode it is possible to avoid too great currentloads on the battery as well as the user.

If the battery has at least one handle, particularly two gripping stripslocated opposite each other, it is possible to manipulate such a batteryparticularly simply, which is known per se.

The method in accordance with the invention for storing a zinc-brominebattery essentially consists in that a directed discharge of the batterywith the electrolytes being circulated is performed and the battery isthen stored in the discharged state. Along with a particularly simpledesign of the battery, such as is required for wide application, aparticularly simple system for storing the battery must also be providedwhich completely prevents damage during storage. This is made possibleby a complete directed discharge, in the course of which the electrolyteis kept circulating to void thermal loads on the battery.

If the electric drive of the pumps for the electrolyte is employed asthe preferably sole user during the directed discharge, it is assuredthat during discharge the electrolyte is compulsorily kept circulating,in which case no additional users are required, for example resistors bymeans of which electrical energy is changed into heat.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in detail below by means of thedrawings:

Shown are in:

FIGS. 1 and 2, two batteries with containers in a schematicrepresentation,

FIG. 3a, an electrode, and

FIG. 3b, a separator, each in a top view, and

FIG. 4, a section of the battery of FIG. 1 along the line IV.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The electro-chemical system, namely the one for a zinc-bromine batterywith circulating aqueous electrolytes and a complexing agent for themolecular bromine, wherein the complexing agent as such iswater-soluble, but the complex itself is hard to dissolve in water, isdescribed in EP-B1 0 167 517, which is a part of the instant invention.

The production of packages of electrodes which are built up ofcarbon-bonded polyethylene and have a frame of an electro-chemicallyinactive material, as well as separators of polyethylene also having awelded frame, wherein the edges of the electrodes as well as theseparators are directly connected with each other, so that a package ofalternating electrodes and separators is created which are weldedtogether at their edges, wherein the electrodes act as bipolarelectrodes, is described in EP-B1 0 167 517, which is a part of theinstant invention.

The zinc-bromine battery shown in FIGS. 1 and 2 in a front and a topview has a package 1 of electrodes and separators arranged one behindthe other. In the embodiment in accordance with FIGS. 1 and 2 theelectrodes 2 as well as the separators 3 are disposed horizontally, asindicated by dashed lines in FIG. 1. The battery is shown in a frontview and in a position of rest in FIG. 1. No dissolution of the zincfilms on the electrodes can occur because no electrolyte is present inthe electrode chambers. Branch lines 4, 5 are located at both ends ofthe cell package and represent the positive and negative poles of thebattery. An electric fuse 40, by means of which electrical overloads andtherefore thermal loads of the battery can be assuredly prevented, canbe disposed between the end contact of one or both electrodes disposedat the end, which in this case are not embodied as bipolar electrodesand instead have a collector grid, for example of silver. In theposition of rest, containers 6 for the anolyte and 7 for the catholyteare disposed below the package 1 of electrodes and separators. In theoperating position the battery is arranged by being turned over in sucha way that the containers come to lie above the package of electrodesand separators. Pump chambers 8 and 9 are disposed in the containers 8and 9, wherein the appropriate pump elements, namely turbine wheels, aredriven by means of the common motor 10 and shafts 11. The pumps aspiratethe electrolyte fluid through an aspirating connector 12 disposed on thebottom in the operating position and pump it via the electrolyte supplylines 14 into the anode or cathode chambers. The electrolyte is returnedback into the container via electrolyte return lines, only partiallyillustrated. As can be seen from the fluid level 15, the containers areembodied such that the entire electrolyte volume can be received in thecontainers, so that during extended periods of idleness the chargedbattery can be stored without having electrolyte in the anode andcathode chambers. The container, the cell package, the pump chambers aswell as the corresponding supply and return lines for the electrolyteare connected with each sealed against gas and fluid, so that twospatial units, namely one for the catholyte fluid and the other for theanolyte fluid, are formed, which are only connected with each other inan electro-chemical manner via separators. Sealing of the pump shaftsagainst the pump chambers, such as it is particularly required inconnection with the embodiment in accordance with FIG. 2, since therethe pump chambers are not disposed inside the electrolyte containers,takes place by means of O-ring seals. The gas- and fluid-sealed closureof the containers can take place via rotatable plugs 16. As representedin FIG. 1, the containers 6 and 7 are connected with each other via apressure equalizer 17. This pressure equalizer has two chambers 18 and19 which are separated from each other by means of a rubber-elasticdiaphragm 20. If there is now a pressure increase in the container 6 or7, the diaphragm 20 is stretched into the chamber 18 or 19 until anappropriate pressure equalization is again assured by the volumeequalization.

With electrodes which are not disposed horizontally, the supply ofelectrolyte takes place in such a way that it enters the lower area ofthe electrode chamber and is drawn off in the upper area. An assuredflow through the electrode chamber is achieved by means of this.Although additional measures for counter flows which flow between theindividual cells via the electrolyte supply and return lines are as arule not required for certain areas of employment, it is possible toprovide known measures, such as the application of counter-potentials tocompensate for leak currents, or blocking elements which prevent theconnection of the individual electrolyte chambers via the electrolyteduring short or prolonged idle times, such as cocks with a plurality ofopenings so that all supply and return lines can be shut or opened withone turn of the cock.

An electrode 2 is represented in FIG. 3a, wherein a central part 21consisting of graphite-bonded polyethylene is surrounded by a frame 22,wherein the elements 21 and 22 are connected flat by welding. Theelement 22 has lower openings 23 and upper openings 24. The frame is ofa greater thickness than the center part, i.e. the actual electrode, sothat a hollow space can be formed by adjoining separators. Branch lines25 and 26 respectively go off the openings 23 and 24 and terminate in adistributor system 27, 28, which is intended to make possible an evendistribution of the electrolyte in the electrode chamber. Preferredareas for the flow are formed by the flow baffles 29, so that an evenflow-through is assured. The two cross-sectional surfaces of theopenings 23 and 24 can either have a continuously even cross section orthey can be such that the inflow is embodied to be tapering or enlargedas a function of the pressure distribution. It is also possible, asknown per se, to provide a compensating flow in this supply line by thearrangement of electrodes at their ends and beginnings.

A separator 3 is illustrated in FIG. 3b having a frame 30 which isessentially electro-chemically inactive and into which the inner part31, the actual separator, is welded. As shown here, it can havecylinder-shaped protrusions 32 which, on the one hand, contribute tostabilizing the electrode chamber and, on the other hand, make turbulentflows in the electrode chamber possible, so that boundary layers of thefluid adhering to the electrodes and separators are released. Theseparators also have openings 23 and 24, which cooperate with thecorresponding ones of the electrodes and form continuous supply linesand return lines.

As can be seen from FIG. 4, the electrodes 2 and separators 3 arerespectively welded together in their edge area 33 so that anode orcathode chambers are created which are respectively bounded by onesurface of the bipolar electrode and the separator.

Such a battery can have a handle, for example, depending on therequirements or can have to gripping strips 41a, 41b so that handlingthe battery is simpler.

Furthermore, such a battery can have a plug connection in place of thetwo branch lines 4, 5, such as is known from other easily portableaccumulators. In this way it is possible to connect such a portableaccumulator for example to drills, hedge clippers, chain saws, but alsoto other portable electric tools. If the accumulators become dischargedeither through use or storage, their charging can take place by means ofa charge device and the normal electrical power supply. It is ofparticular importance in this connection that it is possible to keep thecharge times for zinc-bromine batteries particularly short in comparisonwith other electro-chemical accumulators since high current densitiesare possible, in particular because of the circulating electrolyte.

Such a self-contained battery is particularly suited for lawnmowers. Inthis case it is possible, for example, to either drive the roller or thecutter with which the grass is cut by means of an electric motor whichis turned on with an electric switch. The electric drive for the pumps,namely the motor, is always connected to the voltage of the battery. Inthis way it is assured that, for example at the end of a mowingoperation, the pumps run until the battery is completely electricallydischarged. If required, a switch member can be provided in the circuitbetween the battery and the motor for the pumps, which makes it possibleto take the pumps temporarily out of action. This can be of interest incases where the mowing operation is disrupted, so that no current is tobe generated by the circulation of the electrolyte. Such a switch canhave a time delay element which, for example after five or ten minutes,compulsorily places the pumps into operation again, in which case it isfurthermore necessary that, together with switching the electric motorfor the lawnmower on, the electric circuit for the pump motor is alsoclosed again. In any case, it is assured by means of this that when thebattery is stored, it is changed to the discharged state and thermalloads because of the circulation of the electrolyte are prevented.However, it is then necessary to charge the battery before putting itinto operation. Since zinc-bromine batteries can be exposed torelatively large current loads, a battery with a capacity of 600 W/h ata voltage of 48 Volt can be fully charged within 1 1/2 hours at most.If, however, only an area of for example 100 m² is to be tended, acharge time of approximately 10 minutes is already sufficient.

A lawnmower operated by a zinc-bromine battery has, besides theadvantage of an electric drive, known per se, that there are noadditional emissions, also the particular advantage that thezinc-bromine battery as such achieves an additional noise suppression,since it can cover the motor and is constructed of materials whichconduct sound badly. In this way such a lawnmower, operated by d.c.current, has a noise level of only 51 dB at a distance of approximately1 m.

For peak loads during charging or even during operation it may bedesirable to provide an individual heat exchanger 50 in each electrolytecircuit for heat removal.

I claim:
 1. A zinc-bromine battery comprising:first and second gas- and fluid-proof reservoirs; a first and second motor driven pump; an electrolyte to be circulated by said first and second motor driven pumps; each of said first and second gas- and fluid-proof reservoirs including a pump chamber coupled to a respective one of said first and second motor driven pumps; means for equalizing pressure between said first and second gas- and fluid-proof reservoirs; an electrode chamber including a plurality of bipolar electrodes and a plurality of plastic separators, said separators disposed between said bipolar electrodes, each of said bipolar electrodes and said separators comprising an outer frame and an inner portion, said outer frame having a thickness greater than the thickness of the inner portion; a plurality of electrolyte supply lines coupling said first and second motor driven pumps to said electrode chamber; a plurality of electrolyte return lines coupling said electrode chamber to said first and second motor driven pumps; said first gas- and fluid-proof reservoir comprising a first electrolyte supply line and a first electrolyte return line and said second gas- and fluid-proof reservoir comprising a second electrolyte supply line and a second electrolyte return line; and said pressure equalization means comprising a rubber elastic diaphragm, said diaphragm separating said electrolyte in said first gas- and fluid-proof reservoir from said electrolyte in said second gas- and fluid-proof reservoir, wherein each of said first gas- and fluid-proof reservoir and said second gas- and fluid-proof reservoir further comprise a heat exchanger for removing heat from said electrolyte.
 2. A zinc-bromine battery in accordance with claim 1, wherein said first and second motor driven pumps can be driven by a common motor.
 3. A zinc-bromine battery in accordance with claim 1, wherein a fluid take-up capability of the reservoirs at least corresponds to respective anolyte and catholyte volumes.
 4. A zinc-bromine battery in accordance with claim 1, wherein in the operating position of the battery the reservoirs are disposed above electrodes and separators.
 5. A zinc-bromine battery in accordance with claim 3, wherein in an operating position of the, battery the reservoir are disposed above the electrodes and separators.
 6. A zinc-bromine battery in accordance with claim 1, wherein each reservoir has a closable opening for removing and replenishing the electrolyte fluid.
 7. A zinc-bromine battery in accordance with claim 1, wherein the separators and/or the electrodes have at their edges, welded frames, continuous openings aligned with each other, by means of which continuous channels are formed as electrolyte supply and return lines which respectively have branch lines into the electrode chambers.
 8. A zinc-bromine battery in accordance with claim 1, wherein an electric fuse is disposed between an end contact of an electrode and a branch line to the user.
 9. A zinc-bromine battery in accordance with claim 1, wherein the battery has at least one handle, in particular two strips located opposite each other.
 10. A zinc-bromine battery in accordance with claim 1, wherein a directed discharge of the battery is performed by means of circulating electrolyte and that thereafter the battery is stored in the discharged state.
 11. A zinc-bromine battery in accordance with claim 1, wherein an electrical drive for the first and second motor driven pumps is a powered by directed discharge of said zinc-bromine battery. 